Re: [PATCH v6 2/3] binder: add trace at free transaction.

[Frankie Chang]

On Fri, 2020-07-31 at 11:50 -0700, Todd Kjos wrote:
> On Mon, Jul 27, 2020 at 8:28 PM Frankie Chang
> <Frankie.Chang@xxxxxxxxxxxx> wrote:
> >
> > From: "Frankie.Chang" <Frankie.Chang@xxxxxxxxxxxx>
> >
> > Since the original trace_binder_transaction_received cannot
> > precisely present the real finished time of transaction, adding a
> > trace_binder_txn_latency_free at the point of free transaction
> > may be more close to it.
> >
> > Signed-off-by: Frankie.Chang <Frankie.Chang@xxxxxxxxxxxx>
> > ---
> >  drivers/android/binder.c       |    6 ++++++
> >  drivers/android/binder_trace.h |   27 +++++++++++++++++++++++++++
> >  2 files changed, 33 insertions(+)
> >
> > diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> > index 2df146f..1e6fc40 100644
> > --- a/drivers/android/binder.c
> > +++ b/drivers/android/binder.c
> > @@ -1522,6 +1522,9 @@ static void binder_free_transaction(struct binder_transaction *t)
> >          * If the transaction has no target_proc, then
> >          * t->buffer->transaction has already been cleared.
> >          */
> > +       spin_lock(&t->lock);
> > +       trace_binder_txn_latency_free(t);
> > +       spin_unlock(&t->lock);
> 
> Hmm. I don't prefer taking the lock just to call a trace. It doesn't
> make clear why the lock has to be taken. I'd prefer something like:
> 
> if (trace_binder_txn_latency_free_enabled()) {
c
> }
> 
> And then the trace would use the passed-in values instead of accessing
> via t->to_proc/to_thread.
> 
Then we still add lock protection in the hook function, when trace is
disable ?

Or we also pass these to hook function, no matter the trace is enable or
not.I think this way is more clear that the lock protects @from,
@to_proc and @to_thread.Then, there is no need to add the lock in hook
function.

int from_proc, from_thread, to_proc, to_thread;
 
spin_lock(&t->lock);
from_proc = t->from ? t->from->proc->pid : 0;
from_thread = t->from ? t->from->pid :0;
to_proc = t->to_proc ? t->to_proc->pid : 0;
to_thread = t->to_thread ? t->to_thread->pid : 0;
spin_unlock(&t->lock);
trace_binder_txn_latency_free(t, from_proc, from_thread, to_proc,
to_pid);

> >         binder_free_txn_fixups(t);
> >         kfree(t);
> >         binder_stats_deleted(BINDER_STAT_TRANSACTION);
> > @@ -3093,6 +3096,9 @@ static void binder_transaction(struct binder_proc *proc,
> >         kfree(tcomplete);
> >         binder_stats_deleted(BINDER_STAT_TRANSACTION_COMPLETE);
> >  err_alloc_tcomplete_failed:
> > +       spin_lock(&t->lock);
> > +       trace_binder_txn_latency_free(t);
> > +       spin_unlock(&t->lock);
> >         kfree(t);
> >         binder_stats_deleted(BINDER_STAT_TRANSACTION);
> >  err_alloc_t_failed:
> > diff --git a/drivers/android/binder_trace.h b/drivers/android/binder_trace.h
> > index 6731c3c..8ac87d1 100644
> > --- a/drivers/android/binder_trace.h
> > +++ b/drivers/android/binder_trace.h
> > @@ -95,6 +95,33 @@
> >                   __entry->thread_todo)
> >  );
> >
> > +TRACE_EVENT(binder_txn_latency_free,
> > +       TP_PROTO(struct binder_transaction *t),
> > +       TP_ARGS(t),
> > +       TP_STRUCT__entry(
> > +               __field(int, debug_id)
> > +               __field(int, from_proc)
> > +               __field(int, from_thread)
> > +               __field(int, to_proc)
> > +               __field(int, to_thread)
> > +               __field(unsigned int, code)
> > +               __field(unsigned int, flags)
> > +       ),
> > +       TP_fast_assign(
> > +               __entry->debug_id = t->debug_id;
> > +               __entry->from_proc = t->from ? t->from->proc->pid : 0;
> > +               __entry->from_thread = t->from ? t->from->pid : 0;
> > +               __entry->to_proc = t->to_proc ? t->to_proc->pid : 0;
> > +               __entry->to_thread = t->to_thread ? t->to_thread->pid : 0;
> > +               __entry->code = t->code;
> > +               __entry->flags = t->flags;
> > +       ),
> > +       TP_printk("transaction=%d from %d:%d to %d:%d flags=0x%x code=0x%x",
> > +                 __entry->debug_id, __entry->from_proc, __entry->from_thread,
> > +                 __entry->to_proc, __entry->to_thread, __entry->code,
> > +                 __entry->flags)
> > +);
> > +
> >  TRACE_EVENT(binder_transaction,
> >         TP_PROTO(bool reply, struct binder_transaction *t,
> >                  struct binder_node *target_node),
> > --
> > 1.7.9.5